Color image pick-up system using strip filter

ABSTRACT

A color filter strip arrangement for a color television camera tube which produces luminance and chrominance signals, and in which the chrominance signals are separeted from each other by phase division. A biasing light source is provided for illuminating the color filter to provide a minimum light level against a black frame at the periphery of the filter in order to enable discrimination of chrominance components when the scene being televised is at an extremely low light level. In another embodiment the strip arrangement involves combinations of first and second colors, and has a strip of the first color, a strip of the second color and a black strip. These combinations of strips are, in turn, separated by transparent strips.

This is a continuation application of application Ser. No. 245,085,filed Apr. 18, 1972 and now abandoned.

The present invention relates to color image pick-up systems and moreparticularly to a color image pick-up system using a camera tubeincorporated with a color strip filter.

Several color image pick-up systems of the type employing a camera tubecombined with a color strip filter have been developed, which areadvantageous in their simple and compact constructions. One of suchcolor image pick-up systems utilizes a color strip filter constituted byred, blue and green color strips which is respectively arranged inpredetermined pitches in space frequency. The color strip filter isplaced in close proximity of the faceplate of a camera tube so as tospatially modulate an optical image focused thereon by an opticalarrangement in red, blue and green contents. The image spatiallymodulated is converted by the camera tube into an electric image signalcontaining three components respectively having different fundamentalfrequencies corresponding to the primary three color contents. The colorsignals are separated from one another by filters respectively havingcentral frequencies substantially equal to the three fundamentalfrequencies of the components contained in the image signal. Theseparated components are then converted through a known process into acomposite color video signal including components, e.g., Y, Q and Icomponents. Difficulty has been encountered in fabricating such colorstrip filter including red, blue and green strips since the stripsshould be arranged in three different space frequencies.

Another system utilizes another type of color strip filter whichincludes index strips in addition to the red, blue and green colorstrips. The color strip filter is incorporated with a camera tube in asimilar manner as the above-stated system so as to obtain an imagesignal. This image signal includes an index signal caused by the indexstrip and three color signals. The index signal is utilized forseparating the color signals from one another. It is pointed out thatthe width of each strip of the strip filter should be so narrow as tomake difficult the fabrication of the strip filter since four stripscorrespond a single picture element. It is also pointed out that, in thesystems as stated above, merely a third or fourth amount of lightemitted from the optical image focuses on the strip filter is utilizedfor making the luminance signal which mainly governs the resolutionpower of a video image reproduced by an image reproducing device such asTV receiver.

It is accordingly an object of the present invention to provide a colorimage pick-up system which can produce a composite color video signalwhich contains a luminance signal with a sufficiently large intensity.

It is another object to provide a color image pickup system whichoperates with high fidelity.

It is a further object to provide a color image pick-up system which canproduce a luminance signal with an intensity in dependence onintensities of color components of an optical image to be picked up.

It is a still further object to provide a color image pick-up systemwhich produces color signals of uniform intensity.

It is a still further object to provide a color image pick-up systemwhich has a simple construction.

It is a still further object to provide an image pick-up system using anovel color strip filter which can be readily fabricated.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings in which:

FIG. 1A is a sectional view showing a conventional color image pick-upsystem;

FIG. 1B is an enlarged fragmentary view of a color strip filter used inthe system of FIG. 1;

FIG. 2 is a diagram showing a waveform of an output signal from thesystem of FIG. 1;

FIG. 3 is an enlarged fragmentary view of a color strip filter accordingto the invention;

FIGS. 4A, 4B, 4C and 4D are cross-sectional views showing various typesof target assemblies useful for the present invention;

FIG. 5 is a cross-sectional view of an image signal generator of asystem according to the invention;

FIG. 6 is a graph showing a partial waveform of an output image signalproduced upon impingement of the electron beam upon the target of thecamera tube of FIG. 5;

FIG. 7 is a block diagram of a signal processor with a biasing lightsource to be used with the television camera tube;

FIGS. 8A through 8F are views showing various waveforms appearing in thesignal processor of FIG. 7;

FIG. 9 is an explanatory view for the operation of the system shown inFIGS. 5 and 7;

FIG. 10 is a graph showing a frequency response curve of a vidicon;

FIG. 11 is a graph explaining distortion of an output signal of thevidicon;

FIG. 12 is a graph illustrating luminance and chrominance signalsproduced upon impingement during a line scan;

FIG. 13 is a block diagram of a correcting circuit in the signalprocessor of FIG. 7;

FIG. 14 is a second embodiment of the strip filter element;

FIG. 15 is a graph showing transmissivities of strips of the stripfilter of FIG. 14;

FIGS. 16A through 16D are diagrams showing output signals with respectto positions of the strips when the filter of FIG. 14 is incorporatedwith the image signal generator of FIG. 5;

FIG. 17 is a diagram showing still another strip filter according to theinvention;

FIG. 18 is a block diagram of a signal processor to be used with theimage signal generator when the strip filter of FIG. 14 is employed;

FIG. 19 is a graph showing a frequency spectrum of the chrominanceincluding an infinite number of higher harmonics when mixed with itsreplica delayed by eight cycles of the fundamental frequency of thepower;

FIGS. 20A through 20E are graphs showing various waveforms produced uponimpingment of the electron beam upon the color filter strip of thesecond embodiment; and

FIG. 21 is a graph explaining the filtering operation in the processingmeans of FIG. 18.

Corresponding parts are similarly numbered.

Briefly described, an image pick-up system according to the inventioncomprises an image signal generator including a single camera tubeincorporated with a color strip filter, and a signal processor forconverting an image signal produced by the signal generator into acomposite video signal of a known type. This color strip filter isconstituted by a plurality of white or transparent strips alternatingwith two kinds of color strips, for example, red and blue strips. Theimage signal therefore includes a luminance component caused by thetransparent strips and two color signals caused by the color strips. Inthe signal processor, the luminance and two color signals are separatedfrom each other through phase-detection and then the separated two colorsignals are separated from each other through either phase-detection orfrequency detection.

Referring now to the drawings and more specifically to FIG. 1A, there isshown a typical conventional color image pick-up system which comprisesa color strip filter 10, an object lens 11 for focusing an object 12onto the surface of the color strip filter 10 so that an optical imageof the object 12 is formed on the surface of the strip filter 10 asshown in FIG. 1B. The strip filter 10 includes index strips 27 and red,green and blue strips 24, 25 and 26 which are arranged in cyclicsuccession so that the optical image is spatially modulated when passingthrough the strip filter 10. The index strips are, for example, made ofa fluorescent material and excited by illumination from a light source13 positioned in the vicinity of the strip filter 10. The spatiallymodulated optical image is irradiated onto the faceplate 14 of a vidicon15 which have a target assembly including a transparent electricconductive layer 16 disposed on the back surface of the faceplate 14 anda photo-conductive layer 17. The photo-conductive layer 17 is scanned byan electron beam 18 emitted from an electron gun 19 positioned within anenvelope 20 of the vidicon 15. Since the spatially modulated opticalimage is irradiated on the photo-conductive layer 17, electric chargesare stored in dependence on the conductivity of a point the electronbeam 18 strikes. The electric charges flow through a resistor 21 to theground thereby to generate a voltage signal at a circuit junction 22.The voltage signal is picked-up through a coupling capacitor 23 by asuitable signal processing means.

In FIG. 1B, the color strip filter 10 used in the system in FIG. 1A isillustrated in an enlarged scale, in which the red, green and bluecolored strips and the index strips are designated by 24, 25, 26 and 27,respectively.

In FIG. 2, a waveform of the image signals produced by the vidicon inFIG. 1A is shown, which includes index signal I_(s), red, green and bluecolor signals R_(s), G_(s) and B_(s).

In FIG. 3, a first embodiment of color strip filter 30 used in a systemaccording to the invention is illustrated which includes transparent orwhite strips 31 and red and blue strips 32 and 33. The white strips 31and the color strips 32 or 33 are arranged alternately with one anotherin a direction perpendicular to the longitudinal direction of eachstrip. Although the strips 31, 32 and 33 may respectively have variouswidths, the strips preferably have a common width from half to double asmuch as the diameter of the flying spot to scan an optical image passedthrough the strip filter. When, for example, the effective horizontalscanning width and the diameter of the flying spot are 12.7mm and 20microns, respectively, it is desirable the width of each strip is 20microns. The strips 31, 32 and 33 arranged in such order as mentionedabove are preferably surrounded by a black frame 34. In this instance,it is to be noted that the space frequency of the color strips 32 or 33is, for example, one-fourth to one-eighth times as small as that of thetransparent strips 31, so that, an image signal spatially modulated bythe color strip filter 30 includes a luminance component with a highintensity and frequency and chrominance components with low intensityand frequencies. It is, on the other hand, revealed in physiology thatthe human eyes are more sensitive to the luminance component than to thechrominance components. Therefore, an image signal produced by using thestrip filter of the invention can be converted into a favorable videosignal through a suitable signal processor.

The above-mentioned strip filter 30 may be built in various types oftarget assemblies several of which are exemplified in FIGS. 4A through4D.

In FIG. 4A, the color strip filter 30 is disposed on a transparentsubstrate 40 made of, for example, glass and having thickness of about 2to 3mm when the substrate 40 forms a faceplate of a camera tube. Atransparent electric conductive layer 42 made of a metal oxide such asSnO₂ and InO₂ is disposed on the color strip filter 30. Aphoto-conductive layer 43 is formed on the electric conductive layer 42.

In FIG. 4B, another type of target assembly is shown which comprises thestrip filter 30 disposed on one surface of a fiber optics plate 44. Atransparent electric conductive layer 42 is disposed on the othersurface of the fiber optics plate 44. A photo-conductive layer 43 isfurther disposed on the electric conductive layer 42.

In FIG. 4C, another type of target assembly is shown which includes thecolor strip filter 30 disposed on one surface of a glass plate 40. Atransparent electric conductive layer 42 is disposed on the othersurface of the glass plate 40. A photo-conductive layer 43 is furtherdisposed on the layer 42.

In FIG. 4D, another type of target assembly is shown which includes thecolor strip filter 30 made of, in this case, electric conductivematerial. A photo-conductive layer 43 is disposed on one surface of thefilter 30. The transparent electric conductive layer 42 is disposed onthe other surface of the filter 30. The conductive layer 42 is disposedon the glass plate 40.

In FIG. 5, an image signal generator according to the invention, isillustrated which includes a target assembly 50 with the strip filtershown in FIGS. 3 and 4A to 4D. The target assembly 50 is placed on afaceplate of a camera tube 51 such as vidicon with an envelope 52surrounded by vertical and horizontal deflection coils 53 and 54 and analignment coil 55. An electron gun assembly 56 is positioned in theenvelope 52, which emits an electron beam toward the target assembly 50.The thus emitted electron beam is vertically and horizontally deflectedso as to scan the back surface of the target assembly 50. The targetassembly includes an electric conductive layer which is connectedthrough a resistor R to a positive terminal of a d-c power source Ewhereby the electron beam is accelerated toward the target 50. Anegative terminal of the power source E is grounded. An opticalarrangement 56 is placed in front of the faceplate of the vidicon 51 soas to focus an object or image 57 onto the faceplate of the vidicon 51.The optical arrangement 56 includes an object glass or lens 58 with adiaphragm 59, and a semicircular cylindrical lens 60 interposed betweenthe lens 58 and the faceplate of the vidicon 51. The optical arrangement56 may further includes an annular reflector 61 interposed between thelens 60 and the faceplate, a tubular shielding member 62 interposedbetween the reflector 61 and the faceplate, and one or more bias lightsources 63 placed adjacent to the peripheral wall of the shieldingmember 62. The reflector 61, shielding member 62 and bias light source63 may be omitted, if desired. With this arrangement, light raysradiated from the bias light sources 63 are reflected on the reflector61 and illuminate the faceplate of the vidicon 51 so that an opticalimage focused by the lenses 59 and 60 on the faceplate is applied with acertain brightness. The optical image is converted by the scanning ofthe electron beam emitted from the electron gun 56 into an electricimage signal which appears at a junction 64 and picked up through acoupling capacitor C and an output terminal 65 by a suitable signalprocessor.

FIG. 6 is a graphic illustration of a waveform of the image signalproduced by the image signal generator of FIG. 5, in which the abscissaand ordinate axes respectively represent the time and amplitude. It isapparent that the waveform has maximum values M_(W) which periodicallyappear and minimum values M_(R) and M_(B) interposed between the maximumvalues M_(W). The maximum values M_(W), and minimum values M_(R) andM_(B) respectively correspond with the white, red and blue strips of thestrip filter.

In FIG. 7, a signal processor for converting the image signal producedby the image signal generator of FIG. 5 into a composite video signal isillustrated, which comprises a pre-amplifier 70 having an input terminalconnected to an input terminal 71. The input terminal 71 is to beconnected to the output terminal 65 of the generator of FIG. 5 so thatthe image signal as shown in FIG. 6 is applied to the pre-amplifier 70.An output terminal of the pre-amplifier 70 is connected to inputterminals of a delaying circuit 72 and differentiator 73. An outputterminal of the differentiator 73 is connected to an input terminal of aSchmidt trigger circuit 74 which has an output terminal connected toinput terminals of a limiter 75. The limiter 75 further wave-shapes theoutput signal from the Schmidt circuit 74 into a pulse having sharpleading and trailing edges. The limiter 75 may be omitted, if desired.An output terminal of the limiter 75 is connected to input terminals offirst, second and third sampling pulse generators 76, 77 and 78 whichrespectively produce sampling pulse trains in response to pulses appliedthereto. Output terminals of the sampling pulse generators 76, 77 and 78are connected to input terminals of first, second and third samplinggates, 79, 80 and 81, respectively, An output terminal of the delayingcircuit 72 is connected to an input of a clamping circuit 82 having anoutput terminal connected to the other input terminals of the first,second and third sampling gates 79, 80 and 81. The clamping circuitclamps on an input signal applied thereto to a d-c level. Outputterminals of the sampling gates 79, 80 and 81 are connected to inputterminals of a correction circuit 83 which has output terminalsconnected to input terminals of a wave shaper 84. Output terminals ofthe wave shaper are connected to a matrix circuit 85 which has outputterminals connected to input terminals of a modulator 86. An outputterminal of the modulator 86 is connected to an output terminal 87.

Referring now to FIGS. 8A to 8F, the operation of the signal processorof FIG. 7 is explained hereinbelow.

When the image signal shown in FIG. 6 is applied to the input terminal71, a signal analogous to the image signal appears on the outputterminal of the pre-amplifier 70, which is applied to the delayingcircuit 72 and the differentiator 73. In FIG. 8B, a wave form of thedifferentiated signal from the differentiator 73 is shown which changesits polarity from positive to negative when the image signal takes amaximum M_(W) and, on the contrary, from negative to positive when theimage signal takes a minimum M_(R) or M_(B). The signal shown in FIG. 8Bis applied through the Schmidt trigger circuit 74 to the limiter 75which then produces a pulse signal as shown in FIG. 8C. The outputsignal of the limiter 75 is applied to the first sampling pulsegenerator 76 which then produces first sampling pulses each pulse ofwhich appears at the trailing edges of the pulse signal from the limiter75. The output signal of the limiter 75 is further applied to the secondand third sampling pulse generators 77 and 78 which then respectivelyproduces second and third sampling pulses alternating with one anotherand appearing at leading edges of alternate pulses of the pulse signalfrom the limiter 75, as shown in FIGS. 8E and 8F.

The output signal of the pre-amplifier 70 is, on the other hand, appliedto the delaying circuit 72 which delays the signal by a delay time equalto a total delay time of the differentiator 73, Schmidt trigger circuit74, limiter 75 and the sampling pulse generators 76, 77 and 78. Thedelayed signal from the delaying circuit 72 is delivered to the clampcircuit 82 which superposes on the delayed signal a d-c bias voltagepredetermined on the basis of the magnitude of the image signalcorresponding to the black frame of the color strip filter of FIG. 3.The delayed and biased signal is applied to the first, second and thirdsampling gates 79, 80 and 81 which sample the signal with the first,second and third sampling signals, respectively. The sampled signalsfrom the sampling gates 79, 80 and 81 undergo the correction by thecorrection circuit 83 for removing the distortion in the image signalcaused by the responsiveness of the camera tube in the system of FIG. 5.The sampled and corrected signals are applied to the wave shaper 84which wave-shapes the signals into analogue signals which are envelopesof the corresponding sampled signals, respectively. The wave-shapedsignals are delivered to the matrix circuit 85 which then converts thewave-shaped signals into the known luminance (Y), and color (Q, I)signals. The Y, Q and I signals are then applied to the modulator 86which then modulates the Q and I signals and mixes the modulated Q and Isignals with the Y signal. The mixed signal or a composite color videosignal appears at the output terminal 87.

FIG. 9 illustrates another example of the image signal produced in thegenerator of FIG. 5 through one horizontal scanning of the electron beamon the faceplate of the vidicon 51. Since, in this case, a dark scene isfocused on a portion of the faceplate corresponding to a time intervaltill a time t, the particular portion is irradiated only with the lightrays from the bias light source 63, so that, the image signal has smallamplitudes until the time t. The small amplitude of image signal isexploited by the sampling signal generators in the signal processor inorder to correctly produce the sampling pulse signals. It should benoted that the sampling pulse generator is inoperable without the imagesignal. The luminous intensity of the bias light source 63 is selectedto apply to the faceplate a bias brightness of 5 or 10 percent of ahighest brightness in the focused scene. The bias brightness isfavorable to prevent unwanted occurring fluorescence in the phosphorouslayer to be used in the vidicon.

Since a light scene is focused on another portion of the faceplate, theimage signal has larger amplitudes after the time t as shown in thefigure. When this image signal with maximum values M_(W), and minimumvalues M_(R) and M_(B) is applied to the signal processor of FIG. 7, thewave-shaper 84 produces envelopes shown by a dot and dash line A, brokenline B and phantom line C. The envelopes A, B and C are respectivelyluminance signal, red color signal and blue color signal.

A typical characteristic of a usual vidicon is shown in FIG. 10, inwhich abscissa and ordinate axes respectively represent space frequencyand responsiveness. Hence, when a light input signal having a spacefrequency f_(s) as indicated by a broken curve D is irradiated on thefaceplate of the vidicon, an output signal as indicated by a solid curveE is produced by the vidicon. The correction circuit 83 corrects suchdistortion in the output signal from the vidicon of the generator.

In FIG. 12, waveform of the output signal from the image signalgenerator is shown, which includes maxima indicated by Y₁, Y₂ . . .Y_(n) ₋₁, Y_(n), and Y_(n) ₊₁, and minima indicated by C₁, C₂, . . .C_(n) ₋₁, C_(n) and C_(n) ₊₁. The maximum and minimum values Y_(n) andC_(n) are corrected into values Y_(N) and C_(N) through the followingequations: ##EQU1## ##EQU2## where, k represents the responsiveness ofthe vidicon at the space frequency f_(s).

FIG. 13 shows a circuit arrangement of the correcting circuit 83 of thesignal processor of FIG. 7 which corrects the sampled image signal onthe basis of the above equations. The circuit arrangment includes afirst, second and third holding circuits 90, 91 and 92 having inputterminals connected to the first, second and third sampling gates 79, 80and 81. An output terminal of the holding circuit 90 is connected to oneinput terminal of a first subtractor 93, to an input terminal of afourth holding circuit 94 and to one input terminal of a second adder95. An output terminal of the second holding circuit 91 is connected onone input terminal of a first adder 96 and to one input terminal of asecond subtractor 97. An output terminal of the fourth holding circuit94 is connected to the other input terminal of the second adder 95. Anoutput terminal of the third holding circuit 92 is connected to theother input terminal of the first adder 96 and to one input terminal ofa third subtractor 98. An output terminal of the first adder 96 isconnected to an input terminal of a first attenuator 99 which has anoutput terminal connected to the other input terminal of the firstsubtractor 93. An output terminal of the second adder 95 is connected toan input terminal of a second attenuator 100 having an output terminalconnected to the other input terminal of the third subtractor 98.

Output terminal of the first, second and third subtractors are connectedto input terminals of first, second and third amplifiers 101, 102 and103. Output terminals of the amplifiers 101, 102 and 103 are connectedto the wave-shaper 84.

When, in operation, the sampled luminance and two color componentsY_(n), C_(n) ₋₁ and C_(n) are applied to the first, second and thirdholding circuits 90, 91 and 92 which respectively hold the sampledcomponents applied thereto until the succeeding sampled components areapplied to the holding circuits 90, 91 and 92. The sampled signals C_(n)₋₁ and C_(n) are applied to input terminals of the first adder 96 whichthen produces a signal of amplitude of (C_(n) ₋₁ + C_(n)). The (C_(n)₋₁ + C_(n)) signal is attenuated by a first attenuator into a signalhaving an amplitude of ##EQU3## which is subtracted from the signalY_(n) at the first subtractor 93. An output signal from the firstsubtractor 93 is amplified by the amplifier 101 into ##EQU4##

When, at the succeeding instant, the signals Y_(n) ₊₁, C_(n) and C_(n)₊₁ are applied to the holders 90, 91 and 92, the fourth holder 94 holdsthe signal Y_(n). The signals Y_(n) ₊₁ and Y_(n) from the holders 90 and94 are applied to the second adder 95 which then produces signal(Y_(n) + Y_(n) ₊₁). The signal (Y_(n) + Y_(n) ₊₁) is attenuated by thesecond attenuator 100 into a signal ##EQU5## The signal ##EQU6## and thesignal C_(n) applied to the second subtracter 97 which then produces asignal of ##EQU7## which signal is then amplified by the amplifier 102into ##EQU8## At the further succeeding instant, the amplifier producesa signal of ##EQU9##

FIG. 14 illustrates a color strip filter 110 of a second embodiment ofthe invention. This color strip filter 110 includes transparent or whitestrips 111, color strips alternate with the transparent or white strips.The color strips are red and blue, or magenta, blue, red and black oropaque strips 112, 113, 114 and 115 which are arranged in the ordernamed.

FIG. 15 illustrates transmissivities of the color strips of the filtershown in FIG. 14, wherein the abscissa and ordinate axes respectivelyrepresent the frequency and the transmissivity. Solid curves F and Grespectively represent the transmissivities of the blue color and redcolor strips, and a broken curve H represents the transmissivity of thered and blue color strips.

FIG. 16A diagrammatically shows the strip filter of FIG. 14, and FIGS.16B to 16D show waveforms of a monochrome content, and red and bluecolor contents in an image signal produced by the generator of FIG. 5when the strip filter of FIG. 14 is used in the target assembly of thegenerator of FIG. 5 and a white scene is focused on the faceplate of thevidicon. When, in this instance, a space frequency of the strip filteris assumed to be f_(s), the monochrome or luminance signal has afundamental wave with a frequency of (1/2)f_(s) and the red and bluecolor signals have fundamental waves with frequencies (1/4)f_(s) and(1/8)f_(s) as indicated by broken lines.

The strip filter of FIG. 14 may be substituted for a strip filter shownin FIG. 17, in which a pair of neighboring color strips correspond witheach color strips of the filter of FIG. 14. Even if the strip filter ofFIG. 17 is used in the image signal generator, the generator functionsin the same manner as the strip filter of FIG. 14 is used.

FIG. 18 illustrates a signal processor which is to be combined withgenerator of FIG. 5 in which the strip filter shown in either FIG. 14 orFIG. 17 is used. The processor includes a pre-amplifier 70 to which animage signal with maximum values M_(W) and minimum values M_(C) as shownin FIG. 20A is applied through an input terminal 71 from the generator.The image signal is amplified by the pre-amplifier 70 and then appliedto a delaying circuit 72 and to a differentiator 73. The differentiator73 produces a signal shown in FIG. 20B which changes its polarity frompositive to negative at a time when the image signal takes maximum valueM_(W) and from negative to positive at a time when the image signaltakes a minimum value M_(C). The output signal from the differentiator73 is converted by a Schmidt circuit 74 and a limiter into a pulsesignal as shown in FIG. 20C. The limiter 75 may be omitted, if desired.The pulse signal from the limiter 75 is applied to a first and secondsampling pulse generators 76 and 77. The sampling pulse generators 76and 77 then produce first and second sampling pulses as shown in FIGS.20D and 20E. The amplified image signal from the pre-amplifier 70 is, onthe other hand, delayed by the delaying circuit and thereafter appliedto a biasing circuit 82 which applies a bias voltage to the amplifiedand delayed image signal. The image signal thus processed is applied tofirst and second sampling gates 79 and 81 which sample the image signalwith the first and second sampling signals. The sampled signals from thefirst and second sampling gates 79 and 81 are luminance and chrominancesignals, which are applied to a correcting circuit 83. The correctedchrominance signal is delivered direct to one input terminal of a mixer121 and through a delaying circuit 120 to the other input terminal ofthe mixer 121. The delaying circuit is adapted to delay the signal by atime equal to 8 × 1/f_(s). The delaying circuit 120 and the mixer 121preferably remove higher harmonic components contained in thechrominance signal. The chrominance signal is separated by first andsecond filters 122 and 123 having central frequencies (1/4)f_(s) and(1/8)f_(s) into red and blue color signals. The red color signal fromthe first filter is delayed by a delaying circuit 124 and applied to oneinput terminal of a matrix circuit 85. The blue color signal is applieddirect to the other input terminal of the matrix circuit 85. Theliminance signal is delayed by a delaying circuit 125 and applied to theremaining input terminal of the matrix circuit 85. The matrix circuit 85produces the Y, Q and I signals which are then applied to a modulator86. The modulator 86 produces a composite color video signal on anoutput terminal 87.

It is now apparent that the system of the invention is operable when thered and blue strips are replaced by one another or when the red stripsare substituted for magenta strip and the blue strips for yellow strips.

It is well known in the art that an a-c power including an infinitenumber of higher harmonics when mixed with its replica delayed by eightcycles of the fundamental frequency f_(s) of the power has a frequencyspectrum as shown by a dot and dash line in FIG. 19.

FIG. 21 shows frequency spectrum of the output luminance and chrominanesignals of the correction circuit 83. The luminance signal has an energydistributing as shown by a solid curve 130. The red and blue colorsignals have energies distributing chrominance indicated by broken lines131 and 132. No problem resides in the overlapping of the curves 130 and131 since the luminance and color signals are separated throughphase-detection. It is, however, a problem that the curves 131 and 132overlap one another. Since, in this instance, the color signals passthrough the delaying circuit 120 and the mixer 121 which havetransmission characteristics as indicated by a dot and dash line 134and, therefore, the color signals have energizes as shown by a solidline 135, the frequency spectrums of the red and blue color signals donot overlap one another so that the color signals are completelyseparated from one another by the filters 122 and 123. In order toeffectively achieve such separation of the color components asabove-described, it is generally required that the ratio of the twospace frequencies of the color components be integral and the delay timeof the delaying circuit 120 is a reciprocal of twice greatest commonmeasure of the two space frequencies.

It is to be understood that although the strip filters above exemplifiedhave strips of equal width, the strips may have various widthes, ifdesired.

It is apparent from the foregoing description that the color imagepick-up system according to the invention has the following features:

1. An image signal produced in the system contains a luminance componenthaving a sufficiently large intensity and a relatively narrow frequencyspectrum.

2. The system can produce a luminance signal having an intensity independence on the intensities of color components in the image signal.

3. The system can produce an image signal including chrominancecomponents with sufficiently large frequency range although theluminance component of the image signal has a sufficiently largeintensity.

4. The system can produce an image signal including chrominancecomponents with a uniform intensity.

5. The system makes unnecessitated the registration and the dichroicmirrors necessitated in a multi-tube system, so that a camera tube ofthe system is simple in construction.

While there have been described what at present are considered to be thepreferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention. It is aimed, therefore, inthe appended claims to cover all such changes and modifications whichfall within the true spirit and scope of the invention.

What is claimed is:
 1. A color television transmitter which includes atelevision camera tube having a photoconductive target at one endthereof, an electron gun at the other end thereof to provide an electronbeam towards said target, a color strip filter positioned adjacent saidtarget remote from said electron gun, the color strip filter beingcomposed of a plurality of transparent strips and color strips of firstand second colors, said transparent strips occurring in alternatingsuccession between said color strips and being adapted to produce firstpulses for generation of luminance signal and said color strips beingadapted to produce second pulses for generation of chrominance signalsupon impingement of said electron beam on said target, the improvementcomprising a correcting circuit comprising:a. means for addingsuccessive two pulses of said first pulses and successive two pulses ofsaid second pulses; b. means for attenuating said added pulses by afactor of ##EQU10## wherein k is in the range from zero to unity; c.means for subtracting said attenuated second pulses from said firstpulses and for subtracting said attenuated first pulses from said secondpulses; and d. means for amplifying said subtracting pulses by a factorof ##EQU11## wherein k has the same value as k in item (b).
 2. A colortelevision system comprising, in combination:a. a color televisioncamera tube including an evacuated envelope having a faceplate at oneend, an electron gun at the other end of said envelope, a color filterelement disposed on said faceplate and a photoelectrical elementdisposed inwardly of said color filter element, means for scanningelectrons from said electron gun in a given direction, said color filterelement comprising in combination therewith;a plurality of transparentstrips extending in a direction normal to said given direction toproduce from said photoelectrical element upon scanning of saidelectrons a luminance signal; color strips of first and second colorsand a blend of said first and second colors arranged in alternatingsuccession with said transparent strips and in recurrent groups tothereby produce first and second color signals from said photoelectricalelement upon scanning of said electrons thereacross; and black stripsseparating each of said recurrent groups; b. an output impedanceconnected to said color camera tube; and c. signal processing circuitmeans, including color encoding means, coupled to said output impedanceand responsive to an image signal appearing thereacross for developing acomposite color video signal therefrom.
 3. A color television system asclaimed in claim 2, wherein said filter element comprises subelementalstrips of said first and second colors separated by a subelementaltransparent strip, said first color strip comprises subelemental stripsof black and said first color separated by a subelemental transparentstrip, said second color strip comprises subelemental strips of saidsecond color and black separated by a subelemental transparent strip,and said black strip comprises subelemental strips of black separated bya subelemental transparent strip.
 4. A color television system accordingto claim 2, further including a light source for superimposing anillumination of a predetermined intensity in front of said camera tube.5. A color television system according to claim 2, in which each of saidcolor strips is colored in either one of two colors of the primary threecolors.
 6. A color television system according to claim 2, in which eachof said color strips is colored in black and in either one of the threeprimary colors or the complementary colors of the three primary colors.7. A color television system according to claim 2, in which said colorstrips have two space frequencies different from each other, and saidsignal processing circuit means includes a sampling pulse generatingmeans for producing two sampling pulse trains one of which has the samephase and frequency as said luminance signal and the other of which hasthe same phases and frequencies as said two color signals, samplingmeans for sampling said image signal with said two sampling pulse trainsso as to separate said luminance signal from said two color signals,filtering means for separating the separated two color signals from eachother through filtering in frequency, and matrix and modulating meansfor converting the luminance signal and the separated two color signalsinto said composite color video signal.
 8. A color television systemaccording to claim 7, in which said sampling pulse generating meansincludes a differentiator for differentiating said image signal, acut-off and limiting circuit for cutting off negative portions of thedifferentiated image signal and for amplifying and limiting thedifferentiated and cut-off image signal so as to convert thedifferentiated and cut-off image signal into a reference pulse signal.9. A color television system according to claim 8, which furthercomprises:a clamp circuit for clamping said image signal to apredetermined level.
 10. A color television system according to claim 8,in which said cut-off and limiting circuit is a Schmidt circuit.